Aluminum automotive structural members

ABSTRACT

Disclosed is a method for producing aluminum vehicular structural parts or members such as from molten aluminum alloy using a continuous caster to cast the alloy into a slab. The method comprises providing a molten aluminum alloy consisting essentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.30 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max. Ti, the remainder aluminum, incidental elements and impurities and providing a continuous caster such as a belt caster, block caster or roll caster for continuously casting the molten aluminum alloy. The molten aluminum alloy is cast into a slab which is rolled into a sheet product and then annealed. The sheet has an improved distribution of intermetallic particles (Al—Fe, Al—Fe—Mn or Mg 2 Si) and improved formability. Thereafter, the sheet product is formed into the vehicular structural part or member with sufficient strength and formability required by automotive industry.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Ser. No. 10/926,704,filed Aug. 27, 2004, incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to aluminum alloy vehicular structural parts ormembers and more particularly, it relates to a method of castingaluminum alloy into sheet having good forming characteristics and toforming the sheet into vehicular structural parts or members such asdash panel, floor panel, door panel, window trim, radio bracket,reinforcements for panels, etc.

In many instances, continuous casting of molten aluminum into slabutilizing twin belt, twin roll or block casters is favored over DCcasting because continuous casting can result in substantial energysavings and total conversion cost savings compared to the DC castmethod. In the continuous casting process, molten metal is continuouslyintroduced to an advancing mold and a slab is produced which may becontinuously formed into a sheet product which is collected or woundinto a coil. However, the continuous casting is not without problems.For example, it has been discovered that the alloy composition and theprocessing steps must be carefully controlled in order to have theformability level to avoid cracking during forming and yet have therequisite strength properties in the final product. That is, the alloyand the processing thereof must be carefully controlled to provide sheethaving the formability suited to the fabricating steps necessary to formthe final product or vehicular structural parts. If the alloy andprocessing steps are not controlled, then in the forming steps, fracturecan occur and the formed parts have to be scrapped. Thus, there is agreat need for selection of an aluminum alloy, continuous castingthereof, and thermal mechanical processing methods which provide a sheetproduct having forming characteristics and strength properties whichpermit forming operations such as bending, stamping, deep drawing,stretching or crimping to hold fasteners during production of vehicularstructural parts or members while avoiding problems of fracturing orcracking, for example.

The continuous casting of molten aluminum and rolling slab producedtherefrom into a sheet product is disclosed in various patents. Forexample, U.S. Pat. No. 5,976,279 discloses a process for continuouslycasting aluminum alloys and improved aluminum alloy compositions. Theprocess includes the steps of continuously annealing the cold rolledstrip in an intermediate anneal using an induction heater and/orcontinuously annealing the hot rolled strip in an induction heater. Thealloy composition has mechanical properties that can be variedselectively by varying the time and temperature of a stabilizing anneal.

U.S. Pat. No. 6,264,765 discloses a method and apparatus for casting,hot rolling and annealing non-heat treatment aluminum alloys. The methodand apparatus comprises continuous casting, hot rolling and in-lineinductively heating the aluminum sheet to obtain the mechanicalproperties within the specification tolerance of the hot rolled product.

U.S. Pat. No. 5,985,058 discloses a process for continuously castingaluminum alloys and improved aluminum alloy compositions. The processincludes the step of heating the cast strip before, during or after hotrolling to a temperature in excess of the output temperature of the caststrip from the chill blocks. The alloy composition has a relatively lowmagnesium content yet possesses superior strength properties.

U.S. Pat. No. 5,993,573 discloses a process for continuously castingaluminum alloys and improved aluminum alloy compositions. The processincludes the steps of (a) heating the cast strip before, during or afterhot rolling to a temperature in excess of the output temperature of thecast strip from the chill blocks and (b) stabilization or back annealingin an induction heater of cold rolled strip produced from the caststrip.

U.S. Pat. No. 5,833,775 discloses an aluminum alloy sheet and a methodfor producing an aluminum alloy sheet. The aluminum alloy sheet isuseful for forming into drawn and ironed container bodies. The sheetpreferably has an after-bake yield strength of at least about 37 ksi andan elongation of at least about 2 percent. Preferably the sheet also hasearing of less than about 2 percent.

U.S. Pat. No. 6,086,690 discloses a process of producing an aluminumalloy sheet article of high yield strength and ductility suitable, inparticular, for use in manufacturing automotive panels. The processcomprises casting a non heat-treatable aluminum alloy to form a castslab, and subjecting said cast slab to a series of rolling steps toproduce a sheet article of final gauge, preferably followed by annealingto cause recrystallization. The rolling steps involve hot and warmrolling the slab to form an intermediate sheet article of intermediategauge, cooling the intermediate sheet article, and then warm and coldrolling the cooled intermediate sheet to final gauge at a temperature inthe range of ambient temperature to 340° C. to form said sheet article.The series of rolling steps is carried out continuously withoutintermediate coiling or full annealing of the intermediate sheetarticle. The invention also relates to the alloy sheet article producedby the process.

U.S. Pat. No. 5,244,516 discloses an aluminum alloy plate for discssuperior in Ni—P platability and adhesionability of plated layer andhaving a high surface smoothness with a minimum of nodules andmicropits, said aluminum alloy plate comprising an aluminum alloycontaining as essential elements Mg in an amount more than 3% and equalto or less than 6%, Cu in an amount equal to or more than 0.03% and lessthan 0.3%, and Zn in an amount equal to or more than 0.03% and equal toor less than 0.4%, and as impurities Fe in an amount equal to or lessthan 0.07% and Si in an amount equal to or less than 0.06% in the caseof semi-continuous casting, or Fe in an amount equal to or less than0.1% and Si in an amount equal to or less than 0.1% in the case of stripcasting, and also containing Al—Fe phase intermetallic compounds, withthe maximum size being smaller than 10 μm and the number of particleslarger than 5 μm being less than 5 per 0.2 mm², and Mg—Si phaseintermetallic compounds, with the maximum size being smaller than 8 μmand the number of particles larger than 5 μm being less than 5 per 0.2mm².

U.S. Pat. No. 5,514,228 discloses a method for manufacturing aluminumsheet stock which includes hot rolling an aluminum alloy sheet stock,annealing and solution heat treating it without substantial intermediatecooling and rapid quenching.

In spite of these disclosures, there is a great need for selection ofaluminum alloy and method for producing vehicular parts or membersutilizing a continuous caster, optimized thermal mechanical processing,to provide good strength and levels of formability which permit ease offorming into intricate parts without cracking.

The term “formability” when used herein is used to describe the easewith which a sheet of metal can be shaped through plastic deformation.Formability of a metal can be evaluated by measuring strength,ductility, and the amount of deformation to cause failure.

The term “aluminum” when used herein is meant to include aluminum andits alloys.

The term “automotive” as used herein is meant to include automobile andother vehicular parts or members as described herein and other transportparts or members having similar construction.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved, low costprocess including continuous casting and rolling to continuously producealuminum sheet product having consistent levels of formability.

It is another object of the invention to provide a process includingcontinuously casting a slab and rolling the slab into a sheet productsuitable for use in producing vehicular parts.

It is still another object of the invention to provide a processemploying continuous casting of molten aluminum into slab and rollingthe slab into sheet product for meeting the forming requirements, suchas bending, stamping, stretching or deep drawing of vehicle structuralparts or members.

And yet it is another object of the invention to provide an improvedprocess for producing aluminum sheet product employing a continuouscaster to produce slab, continuously rolling the slab to produce a sheetproduct and annealing the sheet product for forming into vehicularstructural parts or panel members having fasteners such as threadedfasteners attached thereto by crimping the sheet product around thefastener.

It is yet another object of the invention to provide a process forproducing vehicular members such as shallow or deep formed panel memberswhich includes continuously casting an aluminum alloy into a slab,rolling the slab to a sheet product and annealing the sheet producthaving good levels of formability, forming the sheet product into apanel having threaded fasteners attached thereto by crimping to providea formed vehicular member for mechanically fastening to support members,for example.

And yet it is another object of the invention to provide a process forcasting a molten alloy comprising 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. %Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.30 wt. % Fe, 0.1 wt. % max. Cu, 0.25wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max. Ti, the remainderaluminum, incidental elements and impurities, casting the alloy into aslab which is hot rolled and annealed to provide a sheet productsuitable for forming into a vehicular structural part or frame memberwhere good formability is necessary.

In accordance with these objects, there is provided a process forproducing aluminum vehicular structural parts or members from moltenaluminum alloy using a continuous caster to cast the alloy into a slab.The method comprises providing a molten aluminum alloy consistingessentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt.% Si, 0.05 to 0.25 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2wt. % max. Zn, 0.15 wt. % max. Ti, the remainder aluminum, incidentalelements and impurities and providing a continuous caster such as a beltcaster for continuously casting the molten aluminum alloy. The moltenaluminum alloy is cast into a slab having Al—Fe, Al—Fe—Mn or Mg₂Sicontaining intermetallic particles. The slab is rolled into a sheetproduct which is then annealed to provide a sheet product having asubstantially uniform distribution or less striations of intermetallicparticles for improved formability. Thereafter, the sheet product isformed into a vehicular structural part or member such as a panel memberfor a door or hood, for example, having fasteners crimped thereto.

Alternatively, the hot rolled sheet may be cold rolled after hotrolling, and then annealed prior to the forming steps. In yet anotherembodiment, the hot rolled sheet may be annealed or even homogenized andthen cold rolled to a cold rolled sheet product. The cold rolled productcan be annealed to provide a product suited to the various formingsteps.

These and other objects will become apparent from a reading of thespecification and claims appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a continuous caster, hot rolling mill and rollsof sheet material.

FIG. 2 is a flow chart showing steps in the invention.

FIG. 3 is a micrograph showing microstructure of D.C. cast material.

FIG. 4 is a micrograph showing microstructure of sheet material formedby continuous casting (CC) and rolling in accordance with the invention.

FIG. 5 is a schematic of a vehicular rear hatch door or lift gate.

FIG. 6 is a side view of a vehicle showing rear door open.

FIG. 7 is a perspective view showing structural members of a rear hatchdoor separated.

FIG. 8 is a cross-sectional view showing structural members hemmedtogether.

FIG. 9 is a cross-section of a threaded fastener crimped into the metal.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The vehicular structural parts or members, for example, of the inventionare comprised of an aluminum base alloy containing controlled amounts ofmagnesium, iron, silicon and manganese for the required strength andformability in the sheet product produced by the casting andthermomechanical process. The total amounts of the alloying elements arerequired to be controlled to meet the strength requirement withoutcausing casting difficulty in the process. Further, the amount ofalloying elements also is required to be controlled to meet theformability requirements, especially the amount of iron, manganese andsilicon. Al—Fe, Al—Fe—Mn or Mg₂Si intermetallic particles form duringsolidification. That is, the distribution, size and amount of suchintermetallic particles after rolling of continuous cast slab candrastically influence the formability of the sheet material.

The Al—Fe, Al—Fe—Mn or Mg₂Si containing intermetallic particles formduring solidification. The distribution of such intermetallic particlesafter rolling of continuous belt cast aluminum slab can be severelystriated or lined causing forming problems. By comparison, direct chill(D.C.) ingot cast material has a more uniform distribution ofintermetallic particles providing good formability. Striations ofintermetallic particle structure causes stress concentration duringplastic deformation which deteriorate formability of the sheet product.Thus, it is desired that the rolled sheet of the invention has asubstantially uniform distribution or less striations of intermetallicparticles to provide for improved formability.

Accordingly, the aluminum base alloy consists essentially of 2.7 to 3.5wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.3 wt. %Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. %max. Ti, the remainder aluminum, incidental elements and impurities.Preferably, magnesium is maintained in the range of 2.8 to 3.3 or 3.5wt. % and manganese is preferably maintained in the range of 0.1 to 0.25or 0.35 wt. %. Further, preferably iron is maintained in the range of0.05 or 0.10 to 0.25 wt. %, typically 0.05 to 0.2 wt. % and silicon ismaintained in the range of 0.05 to 0.15 wt. %. Impurities are preferablylimited to not more than 0.05 wt. % each and the combination ofimpurities should not be greater than 0.15 wt. % total.

Thus, it will be understood that to use an alloy of the abovecomposition in the process of the invention to form automotive membershaving the requisite properties requires careful control of the alloyingelements in the alloy and the casting thereof to avoid formingintermetallic particle structures adverse to the forming operation. Thatis, it will be appreciated that in the present process, there is greatdifficulty in balancing all the constituents in the alloy for strengthand procedural steps necessary to forming a sheet product havingdesirable properties for forming into the final product while avoidingundesirable properties which leads to fracture or cracking, for example,during the forming process. Further, it should be understood that highmagnesium contents can result in edge cracking during casting andformation of hot rolling holes during processing. Thus, it is importantto keep the magnesium content lower, for example, in the range of 2.7 to3.45. With respect to manganese, iron and silicon, these elements tendto form intermetallic particles during solidification. Thus, incontinuous casting and rolling, heavy striations of intermetallicparticles will be formed if the manganese, iron and silicon are notcarefully controlled. It is important to avoid these particles in orderto have high formability stamping at room temperature. In other alloys,high manganese is needed to prevent grain growth when such alloys areformed at high temperatures.

Not only is it important to have alloying elements and impurities in thecontrolled amounts as herein described, but the slab produced bycontinuous casting, the sheet formed from the slab and automotive memberfabricated from the sheet must be prepared in accordance with specificmethod steps in order to produce sheet and automotive structural partsor members therefrom having the desirable characteristics. That is, theprocess must be controlled in order to produce product having nearformability properties of DC ingot fabricated material without the costpenalties of the DC ingot process.

Thus, referring now to FIG. 1, there is shown a schematic illustrationof a belt caster 2 and rolling mill for producing sheet suitable forforming into vehicular structural parts or members in accordance withthe invention.

In FIG. 1, molten aluminum 10 is provided in a furnace or reservoir 12.Molten aluminum from reservoir 12 is directed along line 14 to a tundish16 from where it is metered through a nozzle 18 into an advancing moldcreated by revolving belts 20 and 22 and side dam blocks (not shown).Belts 20 and 22 are turned by means of rolls 24. Molten metal, e.g.,molten aluminum, is solidified to form a continuous slab 15 betweenbelts 20 and 22 which are chilled using coolant spray 26. Belt caster 2is described in U.S. Pat. Nos. 3,864,973; 3,921,697; 4,648,438;4,940,076 and 4,972,900, incorporated herein by reference as ifspecifically set forth. Improved nozzles for a belt caster are set forthin U.S. Pat. No. 5,452,827, incorporated herein by reference.

Another casting apparatus that may be used in the present invention is ablock caster wherein the blocks are connected to form belts and isincluded herein as a belt caster. As described with respect to beltcaster 2, a tundish and nozzle are provided to transfer molten metal tothe block belts of the block caster wherein solidification occurs toprovide a solidified slab 15 and the blocks are chilled to aid insolidification of the molten metal.

Yet another apparatus that may be utilized to cast a continuous strip orslab 15 is a roll caster which includes two rolls which rotate toprovide the continuously advancing mold. As in the belt caster, atundish and nozzle are used to transfer molten aluminum to the molddefined by the two rolls. Again, the rolls are normally chilled to aidin solidification of the molten metal into a strip or slab. Thedifferent casters are described in U.S. Pat. No. 5,452,827. By the useof the term “continuous caster” is meant to include all these casters.

Molten aluminum alloy of the invention is introduced to the caster in atemperature range of about 1220° to 1320° F., typically 1250° to 1285°F., and exits the caster at a temperature in the range of 750° to 1150°F., typically 860° to 950° F. In addition, typically the continuous slabexiting the belt caster has a thickness in the range of 0.2 to 2 inches,for example, 0.2 to 1 inch. A typical slab thickness for the belt casteris about 0.6 to 0.875 inch. Belt casting speed can range from 10 to 40ft/min, depending on the thickness of the slab. It is important toadhere to these casting conditions in order to obtain microstructureswith less striations or lines of intermetallics such as Al—Fe, Al—Fe—Mnor Mg₂Si for purposes of formability and corrosion resistance. It shouldbe noted that DC cast material normally has good or substantiallyuniform distribution of intermetallic particles. But, as noted earlier,DC cast material has the penalty of higher conversion costs than thesubject continuous cast slab. Thus, the present invention providescontinuous cast slab for forming into sheet material with near DC castproperties to obtain the cost savings and yet retain the desirableproperties such as formability.

After exiting the caster, the slab 15 is directed to rolling mill 30where it is rolled to form a rolled strip or flat product 34 usingpreferably a hot mill. Hot mill 30 is comprised of one or more pairs ofoppositely opposed rolls 32 which reduces the thickness of the slab acontrolled amount as it passes between each stand of rolls. Three setsof hot stands or rolls are illustrated in FIG. 1. For example, slab 15having a thickness of about 0.2 to 1 inch would be reduced to a sheetproduct having a thickness of about 0.01 to 0.25 inch. Typically, forvehicular structural parts or plural panel members the sheet productwould have a thickness in the range of 0.02 to 0.1 or 0.2 inch, forexample, depending on the application. The temperature of the slabentering hot mill 30 would typically be in the range of about 700° to1100° F., if no heat is added. Typically, temperature of sheet productexiting mill 30 would be in the range of 350° to 700° F. In anotheraspect of the invention, the slab from caster 3 may be heated prior tohot rolling (not shown in FIG. 1) to a temperature of 800° to 1100° F.to increase the rolling temperature prior to hot rolling. Thus, slabentering the hot mill can have temperatures of about 800° to 1100° F.

Hot mill 30 can reduce the thickness of the slab about 60 to 95% of itsoriginal thickness, with typical reduction being 75 to 95%. Depending onthe end use of the sheet product, heat may be applied to the strip orslab between hot stands in addition to or instead of heating prior tothe hot mill.

The temperature of the aluminum alloy sheet exiting the hot mill can bein the range of about 400° to 825° F., depending on whether there washeat input before or during hot rolling.

After hot rolling, hot rolled strip 34 can have a deformation textureand deformed grain structure. The hot rolled strip can have a partiallyor fully recrystallized grain structure with an optimum texturedepending on previous heat input and rolling reduction. If the structureremains deformed and a recrystallized grain structure is necessary forthe end product, then annealing of the hot rolled strip 34 can beapplied to promote recrystallization of the deformed structures. Forexample, it is important for automotive application using the aluminumalloy of the invention to have a fine, fully recrystallized grainstructure with random texture for the purpose of forming automotiveparts in accordance with the invention. Thus, in the present invention,it is preferred that the hot rolled sheet be fully annealed to O-temperin annealer 40. Hot rolled sheet in the fully annealed condition canhave a tensile strength in the range of 28 to 35 ksi, a yield strengthin the range of 12 or 13 to 17.5 ksi and an elongation greater than 19%,e.g., 19-30%.

Referring to FIG. 1, it will be seen in the embodiment illustrated thatthe hot rolled sheet product is directed to a continuous annealer 40,using a heater such as an infrared, solenoidal or transverse fluxinduction heater. While any continuous heater may be used, an inductionheater is preferred. Continuous anneal may also be required if coldrolling (not shown in FIG. 1) of the hot rolled strip is necessary.Thus, the hot or cold rolled strip may be continuously annealed inannealer 40 in a temperature range of 600° to 1100° F. in time periodsfrom 0.5 to 60 seconds in order to effect fully recrystallized sheethaving fine grains and highly desired formability properties. However,care is required that the sheet product is not over annealed to thepoint where secondary recrystallization occurs. Secondaryrecrystallization is the growth of fine grains into undesirable coarsegrains which are detrimental to formability.

Instead of continuous annealing, the hot rolled sheet may be batchannealed. That is, hot rolled sheet 42 is wound into coils 48 or 49.These coils are then placed in a furnace and soaked in a temperaturerange of 600° to 1000° F. for 2 to 10 hours to provide the rolled sheetin a fully annealed or O-temper condition. If the slab has been hotrolled to a gauge suitable for forming, then no further thermalmechanical processing is necessary and the sheet is in condition for theforming steps. If the slab has been hot rolled to an intermediate gauge,then after annealing, the annealed material is subjected to cold rollingfollowed by further annealing to provide sheet in the O-temper forforming operations.

After hot rolling, the hot rolled sheet or flat product may be allowedto cool prior to other operations. For example, after hot rolling, withor without annealing and cooling, the resulting strip 42 may be coldrolled (not shown in FIG. 1) to a sheet product having a final gauge.The cold rolling may be performed by passing strip 42 through severalpairs or stands comprising a cold mill to provide the cold rollingrequired to produce the final gauge. Cold rolling can reduce thethickness of strip 42 by 20% to 80% or 90%. Final gauge can range from0.02 to 0.09 or even 0.2 inch, typically 0.03 to 0.12 inch, forautomotive applications. It will be appreciated that the cold rolling,which is rolling at lower than 300° F., can be performed in a coldrolling line separate from the subject continuous casting and rollingline.

After cold rolling to final gauge, the sheet product is subject tofurther anneal to ensure the required crystallographic texture and grainstructure necessary for forming into the final automotive product.

After hot rolling or annealing sheet 42 may be subject to a continuousrapid quenching such as cold water quench 50 prior to furtheroperations. Quench 50, if used and shown after anneal, can be located atdifferent locations in the process.

Referring to FIG. 2, it will be seen that in an alternate processannealed hot rolled sheet may subject cold rolling followed by furtherannealing prior to forming. In a further embodiment or alternateprocess, after hot rolling, the sheet may be directly cold rolledfollowed by annealing of the cold rolled sheet prior to being formedinto a vehicular structural part or member. The cold rolled and annealedsheet, along the rolling direction, can have a tensile strength in therange of 28 to 35 ksi, a yield strength in the range of 12 to 17.5 ksiand an elongation greater than 19%. Further, the finish gage coils maygo through one or combination of steps before the forming process, suchas tension leveling, slitting, surface pretreatment, lubrication orcut-to-length.

As an example of the desirable microstructures which have good formingcharacteristics of continuously cast (CC) aluminum sheet, reference ismade to FIGS. 3 and 4. FIG. 4 shows the microstructure of CC 5754 alloywith controlled chemistry while FIG. 3 shows that of the commerciallyused DC 5754 alloy sheet. Both sheets are 0.060 inch in thickness andare in the O-temper condition. SEM inspection of the particles whichwere formed during solidification shows that they are comprised ofAl—Fe, Al—Fe—Mn and Mg₂Si. The particle structure of CC sheet issubstantially uniformly distributed with only minimal striations orlines while the intermetallic particles of DC sheet are uniformlydistributed. The intermetallic particle size of CC material ranges fromabout 0.1 to 7 μm while that of DC material ranges from about 0.5 to 10μm. The area fraction of intermetallic particles is 0.43% for CCmaterial while the area fraction is 0.56% for DC material. Also, withthe optimum-processing route, CC sheet has a finer grain structure thanDC sheet. The measurement of the grain size shows that CC material hasan average grain size of 16.6 μm while DC material has an average grainsize of 17.8 μm. Grain size for CC material can have a range of 15 to 17μm. Thus, it will be seen that with control of chemistry andoptimization of processing, the continuous cast technology can producemicrostructures which are similar to those produced by the DC casttechnology and thus provides formability properties required byautomotive industry, for example.

Referring now to FIG. 5 there is illustrated an automotive lift gate 100provided as part of a sports utility vehicle (SUV). The lift gate iscomprised of a bottom metal portion 102 and a window frame portion 104covered with glass. Lift gate 100 is mounted to roof 108 of the SUVusing hinges 106 and is closed or secured to the vehicle using handle110. Generally, sides 112, bumper 114 and roof 108 define the openingclosed by the lift gate. In FIG. 6, lift gate 100 is shown partiallyopen and supported by strut 116. Compared to steel, a lift gatefabricated from an aluminum alloy of the invention can result insubstantial weight savings which can be as much as 20 pounds, dependingon the vehicle. Further, lighter and less costly struts can be used toopen and support the lift gate, adding to the weight savings. It will benoted that strut 116 is fastened to lift gate 100 at 118 which requiresthe aluminum alloy to have good forming characteristics to hold athreaded fastener.

FIG. 7 shows an exploded view of an automotive lift gate structurecomprised of an outer panel 120 and an inner panel 122 which areperipherally joined to provide a dual panel lift gate structure. It willbe appreciated that doors, hoods, fenders and the like can employ thesame type of construction, i.e., inner and outer panels. Further, itwill be seen from FIGS. 7 and 8 that outer panel 120 employs a generallycurved, smooth shape. Also from FIG. 7 it will be seen that outer panel120 configuration shows window frame 104 as an integral part of bottomportion 102. Referring further to FIG. 7, it will be noted that innerpanel 122 uses a more complicated design which includes dished portions124 and can have raised channels and open portions (not shown),particularly when used for doors or hoods. The inner panel with itsdished portions and raised portions serves to increase the flexuralstrength of the lift gate. Further, the inner panel or outer panel canbe shaped from a single sheet using stamping between mating dies toprovide the structural features necessary to the lift gate assembly.While the outer panel is relatively smooth and curved, as noted, theinner panel will usually be shaped to form a channel 126 (FIG. 8) toprovide increased strength to the window frame portion. It should benoted that outer panel 120 can be formed of steel or, for example,aluminum alloys AA6111 or AA5083, the composition of which is providedin the Aluminum Association publication entitled “International AlloyDesignations and Chemical Composition Limits for Wrought Aluminum andWrought Aluminum Alloys”, dated January 2001, all of which isincorporated herein by reference as if specifically set forth.

FIG. 8 shows a cross section of a lift gate employing outer panel 120hemmed or seamed to inner panel 122. Thus, outer panel 120 is relativelysmooth and inner panel 122 has recessed areas and employs a channelaround the window frame 104 for increased strength. The lift gatederives its strength from the dual or plural structure of the two formedpanels.

Formed panels can include doors, hoods, trunk lids, fenders, floors,wheels and bumper backup bars and can be formed from flat sheets ofaluminum alloy formed between mating dies to provide a three-dimensionalstructure. The dual or plural structure as depicted employs peripheralseaming or hemming to provide the vehicular structural member; however,other means of joining can include welding, riveting, adhesive bondingand thus the inner and outer panels can be joined by any of thesemethods and such is contemplated. The seaming or hemming referred to isshown in FIG. 8 where outer panel 120 is hemmed around inner panel 122.Thus, outer panel 120 should be capable of forming or bending 180°without cracking where the radius of the bend is about half thethickness of the metal.

In some instances, the structural member may include a combination ofsteel and aluminum alloy, but such structure would not provide the sameweight savings.

The alloy of the invention is required to have good formability for yetanother reason. That is, hinges 106 and struts 116, for example, arepreferred to be joined to steel threaded fasteners. Thus, at 118 wherestrut 116 is connected to lift gate 100, it is preferred to use a metalfastener such as a steel fastener. Accordingly, a threaded fastener 130is crimped into the sheet metal of the inner panel as shown in FIG. 9.The crimping must be of a severity to pull the sheet metal aroundshoulder 132 of the threaded fastener without forming cracks in thesheet metal. The locking of the threaded fastener in the sheet metalmust be sufficiently tight to permit screwing a bolt through an eye inthe strut into the fastener. Crimping in this manner obviates weldingand readily permits joining of aluminum to a steel threaded fastener forease of fabrication. Crimping is alloy sensitive and if the iron is toohigh, the metal can crack during the crimping operation. Thus, forpurposes of crimping, it is preferred to keep iron less than 0.25 wt. %and preferably in the range of 0.05 or 0.1 to 0.2 wt. %.

Thus, aluminum alloy vehicular parts or members produced in accordancewith the foregoing practices provide material having the strength andformability for use as vehicular or automotive sheet which can be formedinto many different automotive structural members.

All ranges provided herein are meant to include all the numbers withinthe range as if specifically set forth, e.g., 1 to 5 would include 1.1,1.2, 1.3, etc., or e.g., 2, 3, 4.

The following example is further illustrative of the invention.

EXAMPLE

An aluminum base alloy containing 3.267 wt. % Mg, 0.201 wt. % of Mn,0.080 wt. % Si, 0.164 wt. % Fe, 0.020 wt. % Cu, 0.004 wt. % Cr and 0.024wt. % Zn, was fed to a twin belt caster at a temperature of 1260° F. andsolidified to produce a 0.875 inch thick slab existing the caster at atemperature of 900° F. The slab was directly fed into a three stand hotrolling mills and rolled to final gauge of 0.100 inch. The temperatureof introducing the slab to the hot rolling mill was at about 820° F. andthe temperature of exiting the mill was at about 520° F. The hot rolledsheet was wound into a coil. The coil was annealed in an anneal furnaceat a temperature of 730° F. for 4 hours. The annealed coil was tensionleveled and slit into the required width and then the coil was given asurface pretreatment and lubricated. The material had properties in therolling direction before forming into automotive parts of: ultimatetensile strength of 32.8 ksi, yield strength of 15.5 ksi, elongation of21.4%. All these properties met the requirement identified by Aluminumfor Automotive Body Sheet Panels, published by The Aluminum Association.The material was formed into inner structural panels, and threadedfasteners were crimped into the sheet with satisfied quality inspection.Thus, the alloy can be cast in a twin belt caster, rolled into a sheetproduct, stamped or shaped into an automotive structural part or memberwith sufficient strength and formability.

It will be seen that the continuous caster can be used to produce a slabwhich can be thermomechanically treated to form a sheet product havingthe properties for forming into vehicular parts or members.

Having described the presently preferred embodiments, it is to beunderstood that the invention may be otherwise embodied within the scopeof the appended claims.

1. In the production of an aluminum automotive structural part or memberfrom a molten aluminum alloy using a continuous caster to cast the alloyinto a slab, the method comprising: (a) providing a molten aluminumalloy consisting essentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. %Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.30 wt. % Fe, 0.1 wt. % max. Cu, 0.25wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max. Ti, the remainderaluminum, incidental elements and impurities; (b) providing a continuouscaster for continuously casting said molten aluminum alloy; (c) castingsaid molten aluminum alloy into a slab having Al—Fe, Al—Fe—Mn or Mg₂Siintermetallic particles; (d) rolling said slab into a sheet product; (e)annealing said sheet product to an O-temper condition, said sheet havingsubstantially uniform distribution or minimized striations of saidintermetallic particles and have an average grain size in the range ofabout 15 to 20 μm; and (f) forming said sheet in said O-temper into saidstructural part or member by stamping at room temperature.
 2. In theproduction of the aluminum structural member in accordance with claim 1wherein manganese is maintained in the range of 0.1 to 0.35 wt. %.
 3. Inthe production of the aluminum structural part or member in accordancewith claim 1 wherein magnesium is maintained in the range of 2.8 to 3.5wt. %.
 4. In the production of the aluminum structural part or member inaccordance with claim 1 wherein iron is maintained in the range of 0.5to 0.25 wt. %.
 5. In the production of the aluminum structural part ormember in accordance with claim 1 wherein said continuous caster is abelt caster, a block caster or a roll caster.
 6. In the production ofthe aluminum structural part or member in accordance with claim 1including annealing said sheet product in a temperature range of 650° to950° F.
 7. In the production of the aluminum structural part or memberin accordance with claim 1 including annealing said sheet product in atemperature range of 700° to 900° F.
 8. In the production of thealuminum structural part or member in accordance with claim 7 includingannealing for about 2 to 10 hours.
 9. In the production of the aluminumstructural part or member in accordance with claim 1 includingcontinuously annealing said sheet product.
 10. In a method for theproduction of an aluminum automotive structural part or member frommolten aluminum alloy using a continuous caster to cast the alloy into aslab, the method comprising: (a) providing a molten aluminum alloyconsisting essentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02to 0.2 wt. % Si, 0.05 to 0.30 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. %max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max. Ti, the remainder aluminum,incidental elements and impurities; (b) providing a continuous casterfor continuously casting said molten aluminum alloy; (c) casting saidmolten aluminum alloy into a slab having a thickness in the range of 0.2inch to 2 inch and having Al—Fe, Al—Fe—Mn or Mg₂Si intermetallicparticles; (d) hot rolling said slab into a hot rolled sheet product,said hot rolling starting in a temperature range of 750° to 1000° F. andending in a temperature of 400° to 825° F.; (e) annealing said hotrolled sheet product to an O-temper condition, said hot rolled sheetproduct in said condition having a tensile strength in the range of 28to 35 ksi, a yield strength in the range of 12 to 17.5 ksi, and anelongation greater than 19% and having substantially uniformdistribution or minimized striations of said intermetallic particles andhave an average grain size in the range of about 15 to 20 μm; and (f)forming said sheet product in said 0-temper condition into saidstructural part or member by stamping at room temperature.
 11. Themethod in accordance with claim 10 wherein magnesium is maintained inthe range of 2.8 to 3.5 wt. %.
 12. The method in accordance with claim10 wherein iron is maintained in the range of 0.05 to 0.25 wt. %. 13.The method in accordance with claim 10 including annealing said hotrolled sheet in a temperature range of 650° to 950° F.
 14. The method inaccordance with claim 10 including annealing said hot rolled sheet in atemperature range of 700° to 900° F.
 15. The method in accordance withclaim 13 including annealing for about 2 to 10 hours.
 16. The method inaccordance with claim 10 including continuously annealing said sheetproduct.
 17. A method for producing aluminum vehicular part or memberfrom molten aluminum alloy using a continuous caster to cast the alloyinto a slab, the method comprising: (a) providing a molten aluminumalloy consisting essentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. %Mn, 0.02 to 0.2 Wt. % Si, 0.05 to 0.30 wt. % Fe, 0.1 wt. % max. Cu, 0.25wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max. Ti, the remainderaluminum, incidental elements and impurities; (b) providing a continuouscaster for continuously casting said molten aluminum alloy into a slabhaving a thickness in the range of 0.2 inch to 2 inch; (c) rolling saidslab into a sheet product having a thickness in the range of 0.01 inchto 0.2 inch; (d) annealing said rolled sheet product to provide a rolledand annealed sheet product having a tensile strength in the range of 28to 35 ksi, a yield strength in the range of 12 to 17.5 ksi and anelongation greater than 19%, said rolled and annealed sheet producthaving a substantially uniform distribution or minimized striations ofsaid intermetallic particles and have an average grain size in the rangeof about 15 to 20 μm; and (e) forming said rolled and annealed sheetinto a vehicular structural part or member by stamping at roomtemperature.
 18. The method in accordance with claim 17 wherein saidrolled sheet product has Al—Fe, Al—Fe—Mn or Mg₂Si intermetallicparticles formed during solidification in a size range of 0.05 to 10 μm.19. A process for producing plural panel automotive members having innerand outer panels connected to form said members, said inner panelshaving threaded fasteners securely crimped into said inner panels toprovide means for bolting accessories to said automotive member, saidinner panel formed by the process comprising: (a) providing a moltenaluminum alloy consisting essentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4wt. % Mn, 0.02 to 0.2 wt. % Si, 0.1 to 0.25 wt. % Fe, 0.1 wt. % max. Cu,0.25 wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max. Ti, the remainderaluminum, incidental elements and impurities; (b) providing a continuouscaster for continuously casting said molten aluminum alloy; (c) castingsaid molten aluminum alloy into a slab having Al—Fe, Al—Fe—Mn or Mg₂Siintermetallic particles; (d) rolling said slab into a sheet product; (e)annealing said sheet product to an O-temper condition, said sheet havingsubstantially uniform distribution or minimized striations of saidintermetallic particles and have an average grain size in the range ofabout 15 to 20 m; (f) forming a portion of said sheet product in saidO-temper into said inner panels by stamping at room temperature toprovide inner panels having raised portions and recessed portions toprovide stiffeners to said inner panels; (g) crimping at least onethreaded fastener to said inner panel; (h) providing an outer panel forjoining to said inner panel; and (i) connecting said outer panel to saidinner panels to provide said plural panel automotive member havingthreaded fasteners joined thereto.
 20. A process for producing pluralpanel automotive members having inner and outer panels connected to formsaid members, said inner panels having threaded fasteners securelycrimped into said inner panels to provide means for bolting accessoriesto said automotive member, said inner panel formed by the processcomprising: (a) providing a molten aluminum alloy consisting essentiallyof 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05to 0.25 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. % max.Zn, 0.15 wt. % max. Ti, the remainder aluminum, incidental elements andimpurities; (b) providing a continuous caster for continuously castingsaid molten aluminum alloy; (c) casting said molten aluminum alloy intoa slab having a thickness in the range of 0.2 inch to 2 inch and havingAl—Fe, Al—Fe—Mn or Mg₂Si intermetallic particles; (d) hot rolling saidslab into a hot rolled sheet product, said hot rolling starting in atemperature range of 750° to 1000° F. and ending in a temperature of4000 to 825° F.; (e) annealing said hot rolled sheet product to anO-temper condition, said hot rolled sheet product in said conditionhaving a tensile strength in the range of 28 to 35 ksi, a yield strengthin the range of 12 to 17.5 ksi, and an elongation greater than 19% andhaving substantially uniform distribution or minimized striations ofsaid intermetallic particles and have an average grain size in the rangeof about 15 to 20 μm; (f) forming a portion of said sheet product insaid O-temper into said inner panels by stamping at room temperature toprovide inner panels having raised portions and recessed portions toprovide stiffeners to said inner panels; (g) crimping at least onethreaded fastener to said inner panel; (h) providing an outer panel forjoining to said inner panel; and (i) connecting said outer panel to saidinner panels to provide said plural panel automotive member havingthreaded fasteners joined thereto.
 21. A process for producing pluralpanel automotive members having inner and outer panels connected to formsaid members, said inner panels having threaded fasteners securelycrimped into said inner panels to provide means for bolting accessoriesto said automotive member, said inner panel formed by the processcomprising: (a) providing a molten aluminum alloy consisting essentiallyof 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05to 0.25 wt. % Fe, 0.1 wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. % max.Zn, 0.15 wt. % max. Ti, the remainder aluminum, incidental elements andimpurities; (b) providing a continuous caster for continuously castingsaid molten aluminum alloy; (c) casting said molten aluminum alloy intoa slab having a thickness in the range of 0.2 to 2 inches thick, saidslab containing Al—Fe, Al—Fe—Mn or Mg₂Si intermetallic particles; (d)hot rolling said slab into a hot rolled sheet product; (e) cold rollingsaid hot rolled sheet product to a thickness in the range of 0.01 inchto 0.2 inch to provide a cold rolled sheet product; (f) annealing saidcold rolled sheet product to provide an annealed sheet product, saidannealed sheet product having a tensile strength in the range of 28 to35 ksi, a yield strength in the range of 12 to 17.5 ksi and anelongation greater than 19%, said annealed sheet product having asubstantially uniform distribution or minimized striations of saidintermetallic particles and have an average grain size in the range ofabout 15 to 20 μm; (g) crimping at least one threaded fastener to saidinner panel; (h) providing an outer panel for joining to said innerpanel; and (i) connecting said outer panel to said inner panels toprovide said plural panel automotive member having threaded fastenersjoined thereto.
 22. A process for producing plural panel automotivemembers having inner and outer panels connected to form said members,said inner panels having threaded fasteners securely crimped into saidinner panels to provide means for bolting accessories to said automotivemember, said inner panel formed by the process comprising: (a) providinga molten aluminum alloy consisting essentially of 2.7 to 3.6 wt. % Mg,0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.25 wt. % Fe, 0.1wt. % max. Cu, 0.25 wt. % max. Cr, 0.2 wt. % max. Zn, 0.15 wt. % max.Ti, the remainder aluminum, incidental elements and impurities; (b)providing a continuous caster for continuously casting said moltenaluminum alloy; (c) casting said molten aluminum alloy into a slabhaving a thickness in the range of 0.2 to 2 inches, said slab containingAl—Fe, Al—Fe—Mn or Mg₂Si intermetallic particles; (d) hot rolling saidslab into a hot rolled sheet product, said hot rolling starting in atemperature range of 750° F. to 1000° F. and ending in a temperaturerange of 450° to 800° F.; (e) annealing said hot rolled sheet product toprovide an annealed sheet product; (f) cold rolling said annealed sheetproduct to a thickness in the range of 0.01 inch to 0.2 inch; (g)annealing said cold rolled sheet product to provide a cold rolled andannealed sheet product having a tensile strength in the range of 28 to35 ksi, a yield strength in the range of 12 to 17.5 ksi and anelongation greater than 19%, said cold rolled and annealed sheet producthaving a substantially uniform distribution or minimized striations ofsaid intermetallic particles and have an average grain size in the rangeof about 15 to 20 μm; (h) forming the said annealed sheet at roomtemperature into said inner panel; (i) crimping at least one threadedfastener to said inner panel; (j) providing an outer panel for joiningto said inner panel; and (k) connecting said outer panel to said innerpanels to provide said plural panel automotive member having threadedfasteners joined thereto.